I compared three methods of determining basal area (cross sectional area of trunks) in this stand of Alaskan birch at the Bonanza Creek LTER site near Fairbanks, Alaska. The diameter of each birch tree was measured in a 42 x 38 m plot surrounding this and two other sample/photo points. This provided a measure of the actual basal area in the plot (30.0 m²/ha). A standard field method (referred to as plotless, prism, or Bitterlich sampling) was used to select trees which subtended at least a threshold angle (1.736°) from this viewpoint. This sample included 13 trees and provided an estimate of basal area of 29.9 m²/ha. An equivalent method was performed on this 360° panoramic image using horizontal pixel counts to represent the subtending angle. Higher precision allowed one additional tree to be included in the sample, and the resulting basal area estimate was 32.1 m²/ha. The field- and image-based methods were repeated at two replicate sample/photo points (see gigapan.org/gigapans/54276/ and gigapan.org/gigapans/54293/). Another gigapan from the south apex after numbered targets were placed is gigapan.org/gigapans/54319/.
This study was presented at the Fine International Conference on Gigapixel Imaging for Science (www.cmu.edu/events/gigapixel-science /). The proceedings paper is available here: fastie.net/wp-content/uploads/2010/11/Fastie-Fine-Conference-m-09-06-10.pdf . Video of the conference presentation is here: www.youtube.com/watch?v=gBQtVZfx9lc&amp;playnext=1&amp;list=PL6D6265673AAA1E78 .